The project is a study of the responses of single units in cortical areas 4, 3a, and 3b of macaca mulatta to wrist flexor and extensor torque pulses or isolated muscle stretch superimposed on a range of steady torques. The aim is to determine the relationships between cortical response to torque pulses or isolated muscle stretch and steady state torque and the relationships between cortical response to torque pulses or isolated muscle stretch and unit behavior during steady state torque. In connection with this project we have developed a technique which permits stretch of individual muscles in the awake behaving primate by direct application of calibrated force unaccompanied by other stimuli. An external electromagnet applied force to a small piece of permeable metal chronically imbedded in the musculotendinous junction. We are using it as an aid in the identification and characterization of units in cortical area 3a, the region to which primary spindle afferents project.